The present invention relates to a reproducing method and a reproducing apparatus for a magneto-optical recording medium which make it possible to detect minute magnetic domains formed on the magneto-optical recording medium, with high resolving power and high S/N ratio. In particular, the present invention relates to a reproducing method and a reproducing apparatus for a magneto-optical recording medium which make it possible to perform reproduction individually in a magnified manner from a plurality of minute magnetic domains existing within a reproducing laser spot when magnetization information is reproduced from minute magnetic domains recorded on the magneto-optical recording medium.
A technique for performing recording and reproduction at a higher density is demanded in view of the increase in amount of information and the advance of the apparatus to acquire a compact size. The magneto-optical recording medium such as a magneto-optical disk is known as an optical memory having a large storage capacity on which information is rewritable. In order to record information on the magneto-optical recording medium, the magnetic field modulation method is used, in which a magnetic field having a polarity corresponding to a recording signal is applied to a portion at which the temperature is raised, while irradiating the magneto-optical recording medium with a laser beam. This method makes it possible to perform overwrite recording, in which high density recording has been achieved. For example, recording has been achieved with a shortest mark length of 0.15 xcexcm. The optical modulation recording system has been also practically used, in which recording is performed by radiating a power-modulated light beam corresponding to a recording signal while applying a constant magnetic field.
However, even when the minute magnetic domain is formed by using the recording system as described above, the following problems arise during reproduction.
(1) Since the spot radius of the reproducing light beam is too large as compared with the size of the recording magnetic domain (recording mark), it is impossible to individually detect a plurality of magnetic domains existing within the reproducing light beam spot. That is, the reproducing resolving power is insufficient. For this reason, it is impossible to reproduce information from individual recording magnetic domains.
(2) Each of recording magnetic domains has a small areal size, and hence the reproduction signal has a small output. For this reason, the reproduction signal has low S/N.
The magnetically induced super resolution (MSR) technique, which has been suggested, for example, in Journal of Magnetic Society of Japan, Vol. 17, Supplement, No. S1, p. 201 (1993), is one of methods to solve the foregoing problem (1). A magneto-optical recording medium used for the magnetically induced super resolution generally comprises a reproducing layer for magnetically induced super resolution, an exchange force control layer, and an information-recording layer. When minute magnetic domains are contained in a reproducing light spot during reproduction, one of the magnetic domains is masked by utilizing the temperature distribution in the reproducing layer so that the other magnetic domain may be individually subjected to reproduction. As described above, in the magnetically induced super resolution, the reproducing resolving power is improved by narrowing the effective field of the radius of the light spot. However, the foregoing problem (2) cannot be solved even by using the magnetically induced super resolution technique, because the intensity of the reproduction signal from each of the magnetic domains does not change.
A reproducing apparatus has been also contrived in order to perform reproduction from recording domains having been subjected to high density recording. Such an apparatus is exemplified by those based on the optical super resolution technique in which a shielding element is inserted into an optical path so that a light-collecting spot which exceeds the diffraction limit of the laser beam is obtained by means of optical super resolution. This technique is discussed in detail in Yamanaka et al., xe2x80x9cHigh Density Optical Recording by Super Resolutionxe2x80x9d, Jan. J. Appl. Phys., 2, Supplement 28-3, 1989, pp. 197-200. Also in this technique, a magnetic mask is generated in the spot by utilizing the fact that the temperature distribution is generated in a magnetic film at the inside of the reproducing light beam spot when an magneto-optical recording medium is irradiated with a reflected light beam. Thus, the effective spot radius, which contributes to the reproduction of the signal, is reduced.
The present inventors have disclosed, in Japanese Patent Application Laid-Open No. 8-7350, a magneto-optical recording medium comprising, on a substrate, a reproducing layer and a recording layer, which makes it possible to magnify and reproduce a magnetic domain transferred to the reproducing layer, by transferring the magnetic domain in the recording layer to the reproducing layer, and applying a reproducing magnetic field during reproduction. An alternating magnetic field is used as the reproducing magnetic field. That is, a magnetic field in a direction to magnify the magnetic domain and a magnetic field in a direction opposite thereto are applied alternately to magnify and reduce respective magnetic domains. The use of the magneto-optical recording medium makes it possible to solve the foregoing problem (2) and amplify the reproduction signal obtained from the magnetic domain. However, it is not easy to control the reproducing magnetic field which is used to magnify the magnetic domain in the reproducing layer. In this viewpoint, this technique requires further improvement. When the magnetic domain is transferred by the aid of the exchange coupling force, the magnification for the magnetic domain effected in the reproducing layer for transferring the magnetic domain thereto is restricted by the size of the magnetic domain in the recording layer. That is, the size of the magnetic domain cannot be magnified to be larger than that of the magnetic domain in the recording layer, at a portion of the reproducing layer on the side of the recording layer. The size of the magnetic domain increases as the separating distance from the recording layer becomes large. Therefore, the following problem arises as well. That is, in an area of the reproducing layer located just over the magnetic domain in the recording layer intended to be reproduced, magnetization is in a direction identical with that in the recording layer in the depth direction for all concerning magnetic domains, however, in an area deviated in the in-plane direction from the magnetic domain intended to be reproduced, a state tends to occur, in which magnetic domain portions having a direction identical with that of magnetization in the recording layer in the depth direction and magnetic domain portions having a direction different therefrom co-exist in a mixed manner.
The present inventors have further disclosed a magneto-optical recording medium and a reproducing method achieved by further developing the technique disclosed in Japanese Patent Application Laid-Open No. 8-7350, in WO 98/02877 and WO 98/02878 disclosed after the priority date of this application. In the reproducing method disclosed in the International Publications, an alternating magnetic field, which is applied during reproduction, is effectively controlled to reliably magnify and reduce the magnetic domain transferred to a magnetic domain-magnifying reproducing layer.
The present inventors have also disclosed, in International Publication WO 97/22969, a method for reproducing information by radiating two types of power-modulated reproducing light beams onto a magneto-optical recording medium comprising a magneto-optical recording film, a first auxiliary magnetic film and a second auxiliary magnetic film composed of a magnetic material which causes transition from in-plane magnetization to perpendicular magnetization when the temperature exceeds a critical temperature. This method successfully reproduce information with an enhanced reproduced signal intensity by transferring a recording magnetic domain in the magneto-optical recording film to the second auxiliary magnetic film with the reproducing light beam having one type of powder and magnifying the transferred magnetic domain. However, the structure of the reproducing apparatus according to the present invention is not disclosed in WO 97/22969. Further, unlike the reproducing method according to the present invention, there is no disclosure concerning the modulation of the power of the reproducing light beam while applying the alternating magnetic field.
Japanese Patent Application Laid-Open No. 6-295479 discloses a magneto-optical recording medium comprising a first magnetic layer and a second magnetic layer (recording layer). The first magnetic layer is a magnetic layer which behaves as an in-plane magnetizable film at room temperature and which behaves as a perpendicularly magnetizable film when the temperature is raised, wherein the transition temperature is increased continuously or in a stepwise manner in the film thickness direction from the side of light incidence. The second magnetic layer is composed of a perpendicularly magnetizable film. The first magnetic layer of the magneto-optical recording medium is composed of a reproducing layer, a first intermediate layer, and a second intermediate layer which are set such that the temperature to cause transition from the in-plane magnetization to the perpendicular magnetization is increased in an order of the reproducing layer, the first intermediate layer, and the second intermediate layer. Therefore, when information is reproduced, the magnetic domain in the recording layer is magnified and transferred to the reproducing layer owing to the relationship concerning the temperature distribution in the reproducing light beam spot and the transition temperatures of the respective layers. However, in this patent document, the reproducing light power is not modulated during reproduction on the magneto-optical recording medium.
FIG. 72 shows an example of a head mechanism to be used for the conventional recording and reproducing apparatus for performing reproduction on the magneto-optical recording medium. An optical head 702 and a magnetic head 703 are arranged opposingly on both side of a recording disk 701 interposed therebetween. Each of the optical head 702 and the magnetic head 703 is relatively large in size and heavy. Therefore, they are supported by a support member 707 and a joint section 711. An engaging section 705, which is attached to the optical head 702 and the joint section 711, is moved on a screw rotary shaft 704 in accordance with rotation of the screw rotary shaft 704 of a driving motor 706. Accordingly, the optical head 702 and the magnetic head 703 can be moved to a desired position on the recording disk 701 to record and reproduce information at this position. In the case of this system, the reproducing apparatus is large and heavy in weight. This system has such drawbacks that it is impossible to respond to the request for the disk recording method and the reproducing apparatus, including, for example, the small size, the light weight, the large capacity, and the high speed of access during recording and reproduction.
On the other hand, a magneto-optical head mechanism 20 shown in FIG. 73 is known as a technique to respond to the realization of a small size of the recording and reproducing apparatus by integrating an optical head and a magnetic head into one unit. In this mechanism 20, a driving unit 713 for an objective lens 710 of an optical head system 712, and a magnetic head slider 714 for arranging a magnetic head coil 721 thereon are combined into one unit. That is, the optical head system 712 and the magnetic head coil 721 are provided on one side of the recording medium 726. A hole 743, through which a converging light beam 738 of a laser beam 709 radiated from the optical head is transmitted, is formed through the magnetic head slider 714. The recording and reproducing apparatus, which is based on the use of such a magneto-optical head, has a considerably small volume. However, such a recording and reproducing apparatus is insufficient to respond to the request for the small size, the light weight, the large capacity, and the high speed of access during recording and reproduction required for the recording and reproducing apparatus. On the other hand, a system is known, in which a head is attached to a tip of an arm, a supporting point for the arm is set to be in the vicinity of a recording medium, and the arm is allowed to swing in parallel to the plane of the disk recording medium so that information is recorded, reproduced, and erased on the disk recording medium. Japanese Patent Application Laid-Open No. 5-54457 suggests a driving system in which an optical head is moved in parallel to the plane of a disk recording medium by using a swing arm or a linear motor. A system for driving an optical head with a swing arm is suggested, for example, in Japanese Patent Application Laid-Open Nos. 8-7309 and 3-203848. A structure, in which a laser beam-reflecting surface is formed on a magnetic head, is suggested in Japanese Patent Application Laid-Open No. 3-280233.
Although these recording and reproducing apparatuses respond to the conventional magneto-optical recording media, they fail to conform with the method for reproducing information with enhanced signal intensity from a recording medium subjected to high density recording, and a magneto-optical recording medium used therefor, as disclosed in Japanese Patent Application Laid-Open No. 8-7350 and WO 97/22969. That is, it is necessary to develop a recording and reproducing apparatus as an apparatus which conforms to the magneto-optical recording medium as recently demanded to realize the small radius, the light weight, the high density, the high recording capacity, and the high speed of recording, reproduction, and erasing. In order to realize the high speed, it is necessary to design the movable direction of the recording and reproducing head to make access to the magneto-optical disk so that the movement is principally effected in parallel to the recording plane of the magneto-optical disk and the movement in the direction perpendicular to the recording plane of the magneto-optical disk is decreased to be as small as possible. In order to realize the small size, it is also demanded to reduce the capacity in the direction perpendicular to the recording plane of the magneto-optical disk. Further, in order to realize further quick access of the recording and reproducing head to the disk, it is necessary to use a head mechanism which is prompt in access and movement action. It is also necessary to make control so that no head crush occurs, for example, due to collision of the recording and reproducing head and the magneto-optical disk.
An object of the present invention is to provide a reproducing method and a reproducing apparatus which are preferably used to perform reproduction on a magneto-optical recording medium of the type in which a recording magnetic domain in an information-recording layer is reproduced by transferring and magnifying it to a reproducing layer, as disclosed, for example, in WO 97/22969. Especially, an object of the present invention is to provide a reproducing method and a reproducing apparatus for a magneto-optical recording medium, in which it is easy to control magnification and reduction of a magnetic domain with a reproducing magnetic field and a reproducing light beam.
Another object of the present invention is to provide a reproducing method and a reproducing apparatus for a magneto-optical recording medium, which make it possible to simultaneously solve the problems (1) and (2) described above and obtain a recorded minute magnetic domain with a high resolving power at a high sensitivity. Still another object of the present invention is to provide a reproducing method and a reproducing apparatus which make it possible to obtain a reproduced signal with sufficient C/N from a magneto-optical recording medium on which minute magnetic domains are recorded.
According to the present invention, there is provided a reproducing apparatus for performing reproduction on a magneto-optical recording medium having an information-recording layer and a reproducing layer, the reproducing apparatus comprising:
a magnetic head which applies a reproducing magnetic field to the magneto-optical recording medium;
an optical head which radiates a reproducing light beam onto the magneto-optical recording medium;
a swing arm which is rotatable about a swing shaft and which supports the optical head at its one end;
a clock generator which generates a reproducing clock; and
an optical head control unit which controls the optical head to radiate reproducing light beams which are power-modulated to have at least two types of light power Pr1 and light power Pr2 on the basis of the reproducing clock, wherein:
the light beam having one power of the light powers Pr1, Pr2 is used to transfer a magnetic domain in the information-recording layer to the reproducing layer and magnify the transferred magnetic domain so that information is reproduced from the magnified magnetic domain in the reproducing layer. The optical head control unit may be, for example, a circuit (RP-PPA) for adjusting the reproducing pulse width and the phase for feeding the control signal to a laser-driving circuit. The reproducing apparatus may further comprise a magnetic head control unit which controls the magnetic head so that an alternating magnetic field is applied on the basis of the reproducing clock. Alternatively, the reproducing apparatus may further comprise a magnetic head control unit which controls the magnetic head so that a DC magnetic field is applied on the basis of the reproducing clock. The magnetic head control unit may be, for example, a reproducing pulse width/phase-adjusting circuit (RP-PPA) for controlling a magnetic coil-driving circuit.
The reproducing method as disclosed in WO 97/22969 can be realized by using the reproducing apparatus according to the present invention. The reproducing apparatus of the present invention is a reproducing apparatus which is necessary when reproduction is performed on any one of magneto-optical recording media according to the first to tenth aspects (first to nineteenth embodiments) described below in order that a magnetic domain recorded in an information-recording layer of each of the magneto-optical recording media is transferred to a reproducing layer (magnetic domain-magnifying reproducing layer), and the transferred magnetic domain is magnified. In the reproducing apparatus of the present invention, the swing arm can be used to move the optical head or the magneto-optical head on the magneto-optical recording medium. Therefore, it is easy to make access to a predetermined recording area, and it is possible to realize a compact size and a light weight of the apparatus. When a solid immersion lens is used for an objective lens of the optical head, it is possible to perform super high density recording. When the present invention is combined with the MAMMOS reproduction and the reproducing light power modulation reproduction, it is possible to realize the super high density recording and reproduction.
The reproducing apparatus may be constructed as follows. That is, the optical head is installed to one end of the swing arm, a reproduced signal-detecting system is installed to the other end, and the swing shaft is provided therebetween. Thus, it is possible to realize a smaller size of the reproducing apparatus.
According to another aspect of the present invention, there is provided an apparatus for performing reproduction on a magneto-optical recording medium having an information-recording layer and a reproducing layer, the reproducing apparatus comprising:
a clock generator which generates a reproducing clock;
an optical head which radiates a reproducing light beam onto the magneto-optical recording medium;
a magnetic head which applies, as a reproducing magnetic field, an alternating magnetic field synchronized with the reproducing clock to the magneto-optical recording medium; and
a swing arm which is rotatable about a swing shaft and which supports the optical head at its one end. The reproducing apparatus includes the magnetic head for applying the alternating magnetic field. Therefore, the reproducing apparatus is preferably used to perform reproduction on the high density magneto-optical recording medium of the type in which the recording magnetic domain in the information-recording medium is transferred to the reproducing layer, and the transferred magnetic domain is magnified to perform reproduction, as disclosed, for example, in WO 98/02877, WO 98/02878, and WO 97/22969. The magnetic field of the alternating magnetic field, which has the same polarity as that of the magnetization of the recording magnetic domain formed in the information-recording layer, may be used to magnify the magnetic domain transferred from the information-recording layer to the reproducing layer, and the magnetic field, which has the polarity opposite to the magnetization of the recording magnetic domain, may be used to reduce the magnified magnetic domain. The reproducing apparatus of the present invention is provided with the swing arm. Accordingly, it is possible to obtain quick access to a desired area. Therefore, the reproducing apparatus of the present invention makes it possible to perform reliable and quick reproduction on the high density magneto-optical recording medium. In order to successfully perform reproduction at a higher density, it is desirable that the optical head is provided with a solid immersion lens as an objective lens. Further, in order to realize a compact size of the reproducing apparatus, it is desirable to use a magneto-optical head in which the magnetic head is incorporated in the optical head.
According to still another aspect of the present invention, there is provided a reproducing method for performing reproduction on a magneto-optical recording medium comprising an information-recording layer and a magnetic domain-magnifying reproducing layer, the method comprising:
radiating a reproducing light beam which is power-modulated to have at least two types of light powers onto the magneto-optical recording medium while applying an alternating magnetic field to reproduce information recorded in the information-recording layer. The alternating magnetic field is applied to the magneto-optical recording medium during the reproduction of information, and the reproducing light beam, which is power-modulated to have at least two types of light powers, is radiated. By doing so, it is easy, as compared with the conventional technique, to set the best condition in order to reliably transfer the magnetic domain from the information-recording layer to the reproducing layer (magnetic domain-magnifying reproducing layer), magnify the magnetic domain, and reduce (extinguish) the magnetic domain. In WO 97/22969, a reproducing light beam, which power-modulated to have two types of light powers, is radiated while applying a DC magnetic field. However, the alternating magnetic field is used in place of the DC magnetic field, and the application timing of the alternating magnetic field and the modulation timing of the optical modulation are appropriately adjusted. Thus, it is easy to find the best reproducing condition which makes it possible to reliably transfer, magnify, and reduce (extinguish) the magnetic domain. When the alternating magnetic field is used, it is possible to reduce (extinguish) the magnified magnetic domain more reliably.
In the reproducing method of the present invention, the reproducing light beam is power-modulated to have the powers Pr1 and Pr2. One of the powers of Pr1 and Pr2 may be used to transfer the magnetic domain in the information-recording layer and magnify the transferred magnetic domain. The other of the powers of Pr1 and Pr2 may be used to reduce or extinguish the magnetic domain magnified in the magnifying reproducing layer. Further, it is possible to radiate the reproducing light beam which is power-modulated to have at least two types of light powers at the same cycle as that of the reproducing clock or at a cycle of integral multiple thereof. The reproducing method of the present invention is extremely useful to perform reproduction on the following magneto-optical recording media according to the first to tenth aspects described below.
Explanation will be made below for the structure and the principle of reproduction concerning the magneto-optical recording media according to the first to tenth aspects.
The magneto-optical recording medium according to the first aspect is a magneto-optical recording medium comprising, on a substrate, an information-recording layer, and a reproducing layer capable of magnifying and reproducing a magnetic domain transferred from the information-recording layer, by applying an external magnetic field having a polarity identical with that of magnetization of the magnetic domain, wherein the information-recording layer has a thickness h which satisfies h/d greater than 0.5 for a radius d of a minimum magnetic domain subjected to recording. That is, when the magneto-optical recording medium of the present invention, which is constructed such that the thickness of the information-recording layer satisfies h/d greater than 0.5, is used, it is possible to realize satisfactory magnification of the magnetic domain. Thus, it is possible to easily control the change in size of the magnetic domain in the reproducing layer with respect to the reproducing magnetic field.
In the magneto-optical recording medium according to the first aspect, the reproducing layer may be composed of a rare earth transition metal in which the compensation temperature is within a range of xe2x88x92100 to 50xc2x0 C. Accordingly, when the magnetic domain, which is transferred from the information-recording layer to the reproducing layer, is magnified and reproduced, it is possible to obtain the magneto-optical recording medium having high resolution and high S/N.
The magneto-optical recording medium according to the second aspect is a magneto-optical recording medium having at least an information-recording layer on a substrate to reproduce information by radiating a reproducing light beam spot, the magneto-optical recording medium comprising, on the substrate, a magnetic layer to perform magnetic domain-magnifying reproduction, a magnetic layer to serve as a gate, and a magnetic layer for recording information in this order, wherein the magnetic layer to serve as the gate is such a layer that only one magnetic domain of a plurality of magnetic domains, subjected to recording in the magnetic layer for recording information and existing within the spot of the reproducing light beam, is transferred from the information-recording magnetic layer on the basis of a temperature distribution in the magnetic layer to serve as the gate generated within the reproducing light beam spot when the magneto-optical recording medium is irradiate with the reproducing light beam spot, and the magnetic layer to perform magnetic domain-magnifying reproduction enables the magnetic domain transferred from the magnetic layer to serve as the gate to be magnified by applying an external magnetic field having a polarity identical with that of magnetization of the magnetic domain.
In the magneto-optical recording medium according to the second aspect, one recording magnetic domain of the plurality of recording magnetic domains in the information-recording layer included in the radius of the reproducing light beam spot is transferred to the gate layer by utilizing the temperature distribution characteristic of the gate layer, the magnetic domain transferred to the gate magnetic layer is transferred to the reproducing layer, and the one domain transferred to the reproducing layer is magnified by using the reproducing magnetic field and detected. Accordingly, the reproducing resolving powder is improved by the gate magnetic layer, and the intensity of the reproduction signal is increased by means of the magnetic domain-magnifying and reproducing technique. Thus, it is possible to improve S/N.
At first, explanation will be made for the principle of the magneto-optical recording medium according to the second aspect of the present invention and a method for reproduction thereon, with reference to FIGS. 1 to 5. FIG. 1A illustratively shows a concept for recording information as minute magnetic domains on a magneto-optical recording medium 11 of the present invention by applying a recording magnetic field 15 while irradiating the magneto-optical recording medium 11 with a recording laser beam 13. The magneto-optical recording medium 11 comprises a magnetic domain-magnifying reproducing layer (reproducing layer) 3, an intermediate layer 4, a gate layer 16, an exchange coupling force control layer 17, and an information-recording layer 18. Information can be recorded on the magneto-optical recording medium 11 based on the use of the magneto-optical field modulation system, wherein the magneto-optical recording medium 11 is irradiated with a laser pulse synchronized with a recording clock while applying a magnetic field having a polarity corresponding to a recording signal. The magneto-optical recording medium 11 is moved in a traveling direction indicated by an arrow in FIG. 1A with respect to a recording laser beam 13. Therefore, an area 19, which is deviated backward from the spot center, is heated to a higher temperature. The magnetization-retaining force or the coercive force of the area 19 in the information-recording layer 18 is lowered due to the heating. Accordingly, a minute magnetic domain, which has a direction of magnetization directed in the direction of the recording magnetic field 15, is formed during its cooling process. It is assumed in the description of the principle that the magneto-optical recording medium is subjected to recording and reproduction by using, for example, a magneto-optical recording and reproducing apparatus 200 conceptually illustrated in FIG. 2. With reference to FIG. 2, the magneto-optical recording medium 210 is rotationally movable with respect to an optical head 213 and a flying magnetic head 215 by the aid of a spindle motor 217, and an initializing magnetic field is applied to the magneto-optical recording medium 210 by the aid of an initializing magnet 211 upon reproduction.
As shown in FIG. 1B, the initializing magnetic field 12 is applied to the magneto-optical recording medium 11, in a direction opposite to the direction of the recording magnetic field 15. The magnetization-retaining force of the gate layer 16 at room temperature is smaller than the initializing magnetic force. Therefore, the magnetic domains subjected to recording in the gate layer 16 are inverted, and all of them are directed in the direction of the initializing magnetic field 12. On the contrary, the magnetization-retaining force of the information-recording layer 18 is extremely larger than the magnetization-retaining force of the gate layer 16. Therefore, magnetization of a recording magnetic domain 313b in the information-recording layer 18 remains as it is. Magnetization of the gate layer 16 is antiparallel to that of the magnetic domain 313b in the information-recording layer 18. Therefore, an interface therebetween is in an unstable magnetization state.
After the gate layer 16 is initialized as described above, the magneto-optical recording medium 11 is subjected to reproduction under a reproducing light beam as shown in FIG. 3. During reproduction, the magneto-optical recording medium 11 is irradiated with the reproducing light beam having a power lower than that of the recording light beam. An area 314, which is deviated backward from the spot center, is heated to a higher temperature in the same manner as heated by the recording light beam. The magnetization-retaining force of the gate layer 16, which corresponds to the area 314 heated to the higher temperature, is lowered. The magnetic domain 313b in the information-recording layer 18 is transferred to the gate layer 16 via the exchange force control layer 17 by the aid of the exchange coupling force between the information-recording layer 18 and the gate layer 16, and it is further transferred to the magnetic domain-magnifying reproducing layer 3. On the other hand, another recording magnetic domain 313a in the information-recording layer 18 is not transferred to the gate layer 16, because an area in the gate layer 16 corresponding to the magnetic domain 313a has a relatively low temperature, and its magnetization-retaining force is not lowered. Therefore, as shown in a lower part of FIG. 3, when the magneto-optical recording medium 11 is enlarged and viewed from an upward position, only an area 315, which has arrived at a high temperature in the laser spot 311, undergoes decrease in magnetic energy. Accordingly, the recording magnetic domain 313b in the information-recording layer 18 appears as a recording mark 316 on the gate layer 16, and it appears on the magnetic domain-magnifying reproducing layer 3. On the other hand, the other magnetic domains 313 are prevented from transfer by the gate layer 16, in areas other than the area 315 in the spot 311. Therefore, the recording magnetic domain 313a in the information-recording layer 18 remains latent. Accordingly, it is possible to independently reproduce only one minute magnetic domain of a plurality of minute magnetic domains existing within the spot size, by irradiating the magneto-optical recording medium with the reproducing light beam in accordance with the principle as shown in FIG. 3.
According to the present invention, one minute magnetic domain, which is focused by using the gate layer 16 as described above, can be transferred to the magnetic domain-magnifying reproducing layer 3, and it can be magnified within the reproducing laser spot. This process is performed in the magnetic domain-magnifying reproducing layer 3 of the magneto-optical recording medium 11. This principle will be explained with reference to FIG. 4A. It is noted that the magnetic domain-magnifying reproducing layer 3 is a magnetic layer to which a minute magnetic domain is transferred from the gate layer 16, and on which the transferred magnetic domain can be magnified by the aid of the reproducing magnetic field. The magnetic domain-magnifying reproducing layer 3 is a perpendicularly magnetizable film having a magnetic force resistance of the magnetization wall which is smaller than the force of the reproducing magnetic field upon being irradiated with the reproducing light beam so that the magnetization wall is moved by application of the reproducing magnetic field to magnify the magnetic domain. When a magnifying reproducing magnetic field 411 is applied in a direction identical with that of magnetization of the minute magnetic domain 313b in the reproducing state shown in FIG. 3, i.e., in the state in which the minute magnetic domain 313b is transferred from the information-recording layer 18 to the gate layer 16 and the magnetic domain-magnifying reproducing layer 3, then the magnetization wall is moved in a direction to magnify the magnetic domain, because the magnetic force resistance of the magnetization wall is small in the magnetic domain-magnifying reproducing layer 3. Thus, a magnified magnetic domain 419 is formed. As a result, as shown in a lower part of FIG. 4A, it is possible to observe a magnified mark 413 (the magnetic domain 419 magnified in the magnetic domain-magnifying reproducing layer) magnified within the reproducing spot 311. As described above, the minute magnetic domain appears after being magnified on the surface of the magneto-optical recording medium. Therefore, a reproduction signal having a sufficient intensity can be obtained from the magnified magnetic domain.
After the magnified magnetic domain 419 in the information-recording layer 18 is subjected to reproduction, a reducing reproducing magnetic field 415 is applied in a direction opposite to that of the magnifying reproducing magnetic field 411 as shown in FIG. 4B. Accordingly, the magnified magnetic domain 419 in the magnetic domain-magnifying reproducing layer 3 is reduced. As a result, areas having a direction of magnetization identical with the direction of the magnetic field of the reducing reproducing magnetic field 415 are predominant. The reducing reproducing magnetic field 415 and the magnifying reproducing magnetic field 411 as described above can be applied by using an alternating magnetic field. A reproduction signal with amplification for each of the minute magnetic domains can be obtained by synchronizing the period or the cycle of the alternating magnetic field with a recording clock.
Now, explanation will be made with reference to a hysteresis curve shown in FIG. 5A for the relationship among the magnitude of the magnifying reproducing magnetic field applied during reproduction, the applied magnetic field, and the size of the mark appearing on the magnetic domain-magnifying reproducing layer 3. The hysteresis curve shown in FIG. 5A illustrates the change in Kerr rotation angle xcex8k of the magnetic domain-magnifying reproducing layer 3 with respect to the magnetic field H. The Kerr rotation angle xcex8k is observed when various magnetic fields H are applied to the magneto-optical recording medium while irradiating the magneto-optical recording medium with a reproducing light beam having the same power as that used during reproduction. It is noted that the hysteresis curve shows a hysteresis curve of the magnetic domain-magnifying reproducing layer of the magneto-optical recording medium having the structure shown in FIGS. 3 to 6, to which the recording magnetic domain in the underlying information-recording layer is transferred by being irradiated with the reproducing light beam. A predetermined Kerr rotation angle xcex8 is provided (point a in FIG. 5) even when the magnetic field H is zero, because the magnetic domain in the information-recording layer has been already transferred. When the magnetic field H having a polarity identical with the polarity of magnetization of the recording magnetic domain is gradually applied, the initial magnetization curve rises. The point b represents an initial rising point. The rise of the initial magnetization curve corresponds to magnification of the magnetic domain in the layer (the magnetic domain 419 in FIG. 4A) as a result of movement of the magnetization wall of the magnetic domain-magnifying reproducing layer 3 from the center of the magnetic domain toward the outside depending on the magnitude of the magnetic field H. In the initial magnetization curve, no more increase in Kerr rotation angle occurs when magnetization is saturated. In FIG. 5A, conceptual photomicrographs of magnetic domain patterns are shown, in which the magnetic domain-magnifying reproducing layer 3 is viewed from an upward position, at respective points including the points a and b on the initial magnetization curve of the hysteresis curve. The magnetic domain pattern (black circle pattern) at the point a concerns magnetic domains obtained when magnetic domains (seed magnetic domains) in the information-recording layer 18 are transferred via the gate layer 16 to the magnetic domain-magnifying reproducing layer 3 by the aid of irradiation with the reproducing light beam. The patterns at the respective points comprehensively suggest the situation in which the magnetic domains are magnified in accordance with the increase of the magnetic field on the initial magnetization curve starting from the state represented by the point a. When the Kerr rotation angle xcex8 is saturated, the magnetic domains are inverted on the entire surface of the magnetic domain-magnifying reproducing layer 3.
In the hysteresis curve shown in FIG. 5A, the magnetic field at the rising point c of the major loop of the hysteresis curve (outer loop which represents a locus after the initial magnetization curves is once saturated), which has the same polarity as that of the magnetic field applied in the direction to magnify the magnetization of the magnetic domain-magnifying reproducing layer, is referred to as xe2x80x9cnucleation magnetic fieldxe2x80x9d. The absolute value thereof is represented by Hn. The magnetic field at the initial rising point b of the initial magnetization curve, which is obtained by applying the magnetic field in the direction to expand the recording magnetic domain in the magnetic domain-magnifying reproducing layer 3 transferred from the information-recording layer 5 via the gate layer 16, is referred to as xe2x80x9cmagnetization wall-magnifying magnetic fieldxe2x80x9d. The absolute value thereof is represented by He. Assuming that the reproducing magnetic field has its absolute value Hr, it is desirable to apply the reproducing magnetic field within a range of He less than Hr less than Hn because of the following reason. That is, if Hr is smaller than He, the recording magnetic domain transferred to the magnetic domain-magnifying reproducing layer 3 is not magnified. If Hr is larger than Hn, even when no recording magnetic domain (seed magnetic domain) exists in the information-recording layer 18, then the magnetic domain in the magnetic domain-magnifying reproducing layer 3 disposed thereover is inverted, and it is read as a signal.
FIG. 5B shows an initial magnetization curve obtained when the magnetic field is applied in a direction to reduce the recording magnetic domain in the magnetic domain-magnifying reproducing layer 3 transferred via the gate layer 16 from the information-recording layer 18, in the hysteresis curve shown in FIG. 5A. The magnetic field at the initial dropping point c of the major loop (outer loop which represents a locus after the initial magnetization curve is once saturated) of the hysteresis curve, which is located on the side of the same polarity as that of the initial magnetization curve, is referred to as xe2x80x9cnucleation magnetic fieldxe2x80x9d. The absolute value thereof is represented by Hn. The magnetic field at the dropping point d on the initial magnetization curve is referred to as xe2x80x9cmagnetization wall-reducing magnetic fieldxe2x80x9d. The absolute value thereof is represented by Hs. When the magnetic field is applied within a range of Hs less than Hr, the magnetic domain having been subjected to magnification and reproduction can be reduced. In FIG. 5B, conceptual photomicrographs of magnetic domain patterns are also shown, in which the magnetic domain-magnifying reproducing layer is viewed from an upward position, at respective points including the points a and d on the initial magnetization curve of the hysteresis curve. Since the magnetic field in the reducing direction is too large at the point e, the recording magnetization transferred to the magnetic domain-magnifying reproducing layer completely disappears. Therefore, when it is intended to reliably erase the recording magnetization, it is appropriate to adjust the magnetic field to satisfy Hs less than Hn less than Hr. The hysteresis curves depicted in FIG. 5A and FIG. 5B and hysteresis curves referred to herein are hysteresis curves obtained under the condition in which magneto-optical reproduction is performed in accordance with the reproducing method for the magneto-optical recording medium of the present invention, and they represent characteristics of the Kerr rotation angle (or magnetization) with respect to various magnetic fields, obtained when the reproducing light beam is radiated and the temperature is raised by actually using the recording and reproducing apparatus for the magneto-optical recording medium. Therefore, the hysteresis curves, Hs, Hn, and Hr to be applied are observed by using a practical magneto-optical recording and reproducing apparatus while radiating the reproducing light beam having the power for reproduction.
According to the present invention, owing to the provision of the gate layer as described above, only one magnetic domain is allowed to emerge on the gate layer 16, or it can be transferred to the gate layer 16 even when a plurality of magnetic domains exist in the information-recording layer. Further, the one minute magnetic domain having been transferred to the gate layer 16 can be transferred to the magnetic domain-magnifying reproducing layer 3, and it can be magnified and detected (reproduced) by using the reproducing magnetic field. Therefore, the minute magnetic domain formed in accordance with the magneto-optical field modulation system can be subjected to reproduction at a high resolving power and at high S/N.
The principle has been explained above by illustrating the gate layer as the magnetic layer which undergoes temperature distribution of the gate layer generated in the reproducing light beam spot, in which the magnetic domain in the information-recording layer is transferred to the gate layer in a high temperature area having a temperature higher than a predetermined temperature. However, it is possible to use a magnetic layer which undergoes the temperature distribution in the gate layer generated in the reproducing light beam spot, in which the magnetic domain in the information-recording layer is transferred to the gate layer in a low temperature area having a temperature lower than a predetermined temperature. Alternatively, it is possible to use a magnetic layer which undergoes the temperature distribution in the gate layer generated in the reproducing light beam spot, in which the magnetic domain in the information-recording layer is transferred to the gate layer in a predetermined temperature range.
The magneto-optical recording medium according to the third aspect is a magneto-optical recording medium comprising a recording layer for recording information therein, a non-magnetic layer, and a reproducing layer, wherein:
magnetization is transferred from the recording layer to the reproducing layer in accordance with magnetostatic coupling by heating the magneto-optical recording medium to a predetermined temperature, and a magnetic domain having the transferred magnetization is magnified for reproduction to be larger than a magnetic domain subjected to recording in the recording layer under a reproducing external magnetic field.
In the magnetic domain-magnifying reproducing technique disclosed in Japanese Patent Application Laid-Open No. 8-7350, the recording layer, the intermediate magnetic layer, and the reproducing layer are magnetically coupled to one another by allowing the intermediate magnetic layer to intervene between the recording layer and the reproducing layer. However, in the magneto-optical recording medium according to the third aspect of the present invention, the recording layer and the reproducing layer are magnetostatically coupled to one another by allowing the non-magnetic layer to intervene between the recording layer and the reproducing layer.
The magneto-optical recording medium according to the fourth aspect is a magneto-optical recording medium comprising a recording layer for recording information therein, an intermediate layer, and a reproducing layer, for reproducing information by detecting a magnetization state of a magnetic domain transferred from the recording layer to the reproducing layer, wherein:
a minimum stable magnetic domain radius in the reproducing layer is larger than a size of a magnetic domain subjected to recording in the recording layer.
In the magneto-optical recording medium according to the fourth aspect, the minimum stable magnetic domain radius in the reproducing layer is larger than the size of the magnetic domain subjected to recording in the recording layer. Therefore, the magnetic domain transferred to the reproducing layer is magnified to be larger than the recording magnetic domain. Accordingly, a reproduction signal having high C/N is obtained by reading magnetization information from the magnified magnetic domain as described above. The magneto-optical recording medium according to this aspect is different from the magneto-optical recording media according to the first to third aspects, in which the magnetic domain transferred from the recording layer to the reproducing layer can be magnified even when no reproducing magnetic field is applied. Accordingly, reproduction can be performed by using a reproducing apparatus constructed in the same manner as the conventional technique.
The intermediate layer of the magneto-optical recording medium according to the fourth aspect may be a magnetic layer or a non-magnetic layer. That is, when the intermediate layer is a magnetic layer, the recording magnetic domain in the recording layer is transferred to the reproducing layer by the aid of the exchange coupling effected by the recording layer, the intermediate layer, and the reproducing layer. When the intermediate layer is a non-magnetic layer, the recording magnetic domain in the recording layer is transferred to the reproducing layer by the aid of the magnetostatic coupling effected between the recording layer and the reproducing layer.
In the magneto-optical recording media according to the first, second, and fourth aspects of the present invention, when the intermediate layer (the intermediate magnetic layer or the gate layer), which is inserted between the reproducing layer (the magnifying reproducing layer) and the recording layer (the information-recording layer), is a magnetic layer, it is desirable that the thickness of the intermediate layer is not less than the thickness of the magnetization wall of the magnetic domain in the intermediate layer, because of the following reason. That is, for example, when a magnetic film, which exhibits in-plane magnetization at room temperature and which makes transition from in-plane magnetization to perpendicular magnetization at a temperature not less than a predetermined temperature (critical temperature), is used for the intermediate layer, it is necessary that the magnetic spin is twisted by 90 degrees in the magnetization wall (hereinafter referred to as xe2x80x9cmagnetization wall of the intermediate layerxe2x80x9d) between the magnetic domain in which the transition occurs and the magnetic domain adjacent to the foregoing magnetic domain, in order to effect the transition. The thickness of the magnetization wall can be measured, for example, in accordance with the following operation based on the use of the Hall effect. The intermediate layer, the reproducing layer, and the recording layer are magnetized in one direction to measure the Hall voltage (V2) at this time. Assuming that the Hall resistances and the thicknesses of the films (layers) of the intermediate layer, the reproducing layer, and the recording layer are xcfx811, xcfx812, xcfx813, t1, t2, and t3 respectively, the Hall voltage V3 obtained when there is no interface magnetization wall is V3=Ixc3x97(t1xcfx811+t2xcfx812+t3xcfx813)/(t1+t2+t3)2, wherein I represents the current flowing into the film (layer). Therefore, the difference (V4) between the absolute value |V1xe2x88x92V2| of the voltage including the interface magnetization wall and 2V3 represents the thickness of the interface magnetization wall. It is also possible to estimate the magnetic spin state which indicates the Hall voltage V4, by using the exchange stiffness constant, the perpendicular magnetization anisotropy energy constant, and the saturation magnetization of the respective layers. Such a method for calculating the interface magnetization wall is described in R. Malmhall, et al., Proceedings of Optical Data Strange, 1993, pp. 204-213. Reference may be made to this document. In the present invention, it is desirable that the thickness of the intermediate layer is not less than the thickness of the magnetization wall measured in accordance with the measuring method based on the use of the Hall effect as described above. For example, when the magnetic material of the intermediate layer is composed of a GdFeCo system such as GdxFeyCoz (20xe2x89xa6X 35, 50xe2x89xa6Yxe2x89xa6100, 0xe2x89xa6Z xe2x89xa650), the thickness of the magnetization wall is calculated to be about 50 nm on the basis of the calculating method described above. Therefore, when the intermediate layer is composed of GdxFeyCoz (20xe2x89xa6X 35, 50xe2x89xa6Yxe2x89xa6100, 0xe2x89xa6Zxe2x89xa650), the thickness of the magnetic layer is required to be not less than 50 nm.
As described above, the thickness of the magnetization wall differs depending on the type and the composition of the magnetic material for the intermediate layer (or the gate layer). However, in the case of the magnetic material to be used for a magnetic layer of the magneto-optical recording medium, the thickness is generally required to be 10 nm at minimum. Therefore, it is preferable that the thickness of the intermediate layer exceeds 10 nm. The upper limit of the thickness of the intermediate layer is preferably less than 100 nm, due to the limitation for the semiconductor laser power. Accordingly, it is preferable for the thickness t of the intermediate layer to satisfy 10 less than t less than 100 nm.
In the magneto-optical recording media according to the first, second, and fourth aspects of the present invention, when the intermediate layer is the magnetic layer, it is preferable that the size of the magnetic domain magnetically transferred from the recording layer to the intermediate layer (gate layer) is smaller than the size of the recorded magnetic domain, in order to stabilize the magnetic domain transferred from the recording layer to the intermediate layer (gate layer).
When information, which is recorded on the magneto-optical recording medium according to the first aspect, is reproduced, the reproduction may be performed by transferring a magnetic domain subjected to recording in an information-recording layer to a magnetic domain-magnifying reproducing layer by irradiating the magneto-optical recording medium with a reproducing light beam, and magnifying the transferred magnetic domain to be larger than a size of the magnetic domain subjected to recording in the information-recording layer to perform the reproduction by applying a reproducing magnetic field having a polarity identical with that of magnetization of the transferred magnetic domain. In this aspect, it is preferable that an alternating magnetic field synchronized with a reproducing clock is used as the reproducing magnetic field, the transferred magnetic domain is magnified by using a magnetic field having a polarity identical with that of magnetization of the magnetic domain subjected to recording in the information-recording layer, and the magnified magnetic domain is reduced by using a magnetic field having a polarity opposite thereto.
In the method described above, a plurality of recording magnetic domains in the information-recording layer capable of being included in a spot of the reproducing light beam may be individually transferred to the magnetic domain-magnifying reproducing layer, and the transferred magnetic domain may be magnified to be larger than the size of the magnetic domain subjected to recording in the information-recording layer to perform the reproduction by applying a reproducing magnetic field having a polarity identical with that of magnetization of the transferred magnetic domain.
In the present invention, when information, which is recorded in a recording area of the magneto-optical recording medium according to the second aspect of the present invention, is reproduced, the reproduction may be performed by transferring a magnetic domain subjected to recording in an information-recording layer to a magnetic domain-magnifying reproducing layer via a gate magnetic layer by irradiating the magneto-optical recording medium with a reproducing light beam, and magnifying the transferred magnetic domain to be larger than a size of the magnetic domain subjected to recording in the information-recording layer to perform the reproduction by applying a reproducing magnetic field having a direction identical with that of magnetization of the transferred magnetic domain. According to this method, one magnetic domain is selected via the gate layer from a plurality of recording magnetic domains in the information-recording layer included in the spot of the reproducing light beam during the reproduction, the generated one magnetic domain is transferred to the magnetic domain-magnifying reproducing layer, and the transferred magnetic domain can be magnified to be larger than the size of the magnetic domain subjected to recording in the information-recording layer to perform the reproduction by applying the reproducing magnetic field in the same direction as that of the magnetization of the transferred magnetic domain.
According to the present invention, when information, which is recorded on the magneto-optical recording medium, is reproduced by the aid of the magneto-optical effect, the reproduction may be performed by using, as the magneto-optical recording medium, a magneto-optical recording medium comprising, on a substrate, an information-recording layer, and a magnetic domain-magnifying reproducing layer for transferring a magnetic domain in the information-recording layer thereto and magnifying the transferred magnetic domain by the aid of an external magnetic field, and magnifying the magnetic domain transferred from the information-recording layer to the magnetic domain-magnifying reproducing layer to be larger than a size of the magnetic domain subjected to recording in the information-recording layer to perform the reproduction by applying, during the reproduction, at least one of a reproducing magnetic field modulated on the basis of a reproducing clock and a reproducing light beam modulated on the basis of the reproducing clock, to the magneto-optical recording medium. The intensities of the reproducing magnetic field and the reproducing light beam are simultaneously modulated during the reproduction, and thus the error rate of a reproduction signal can be further lowered.
In the reproducing method according to the present invention, the reproducing magnetic field has its absolute value Hr which relates to an absolute value Hn of the nucleation magnetic field of the hysteresis curve of the magnetic domain-magnifying reproducing layer as explained with reference to FIG. 5, an absolute value He of the magnetization wall-magnifying magnetic field, and an absolute value Hs of the magnetization wall-reducing magnetic field, as measured by using a reproducing power of a recording and reproducing apparatus, such that the reproducing magnetic field is applied to satisfy He less than Hr less than Hn in a magnifying direction and Hs less than Hr in an erasing direction. If a magnifying magnetic field having an intensity not less than Hn is applied, then the magnetization in the reproducing layer is inverted even at portions in which no information is recorded in the information-recording layer, and it is impossible to detect any recording signal, which is not preferred. When a reducing magnetic field having an intensity larger than Hs is applied, the magnetic domain in the reproducing layer is erased. In principle, the magnifying reproduction is not obstructed even when the magnetic domain in the reproducing layer is not completely erased. However, the signal efficiency is rather improved when the magnetic domain is completely erased.
The magneto-optical recording medium according to the fifth aspect is a magneto-optical recording medium comprising at least a magneto-optical recording layer for recording information thereon, a first auxiliary magnetic layer, and a second auxiliary magnetic layer, for magnifying and transferring a recording magnetic domain recorded in the magneto-optical recording layer via the first auxiliary magnetic layer to the second auxiliary magnetic layer when the magneto-optical recording medium is irradiated with a reproducing light beam, and reproducing information from the magnified and transferred magnetic domain in the second auxiliary magnetic layer, wherein the first auxiliary magnetic layer has a thickness which is not less than a thickness of a magnetic wall of the first auxiliary magnetic layer.
The magneto-optical recording medium according to the sixth aspect is a magneto-optical recording medium comprising at least a magneto-optical recording layer for recording information thereon, a first auxiliary magnetic layer, and a second auxiliary magnetic layer, for magnifying and transferring a recording magnetic domain recorded in the magneto-optical recording layer via the first auxiliary magnetic layer to the second auxiliary magnetic layer when the magneto-optical recording medium is irradiated with a reproducing light beam, and reproducing information from the magnified and transferred magnetic domain in the second auxiliary magnetic layer, wherein the first auxiliary magnetic layer has a thickness which exceeds 10 nm.
Main components of the magneto-optical recording media according to the fifth and sixth aspects are conceptually shown in FIGS. 41A and 41B by way of example. The magneto-optical recording medium has a structure in which a first auxiliary magnetic layer 405 and a second auxiliary magnetic layer 404 are stacked successively on a magneto-optical recording layer 406. Each of the first auxiliary magnetic layer 405 and the second auxiliary magnetic layer 404 has such a magnetic characteristic as shown in FIG. 42 that the layer behaves as an in-plane magnetizable layer at a temperature from room temperature to a certain temperature (critical temperature) TCR which is not less than room temperature, and the layer behaves as a perpendicularly magnetizable layer at a temperature which is not less than TCR. The magneto-optical recording layer 406 exhibits perpendicular magnetization in a wide temperature range including room temperature. Assuming that the Curie temperatures of the magneto-optical recording layer 406, the first auxiliary magnetic layer 405, and the second auxiliary magnetic layer 404 are TC0, TC1, and TC2 respectively, and the critical temperatures of the first auxiliary magnetic layer and the second auxiliary magnetic layer are TCR1 and TCR2 respectively, the magnetic characteristic of the magneto-optical recording medium satisfies the relationship of room temperature  less than TCR2 less than TCR2 less than TC0, TC1, TC2.
Explanation will be made below for the principle of reproduction on the magneto-optical recording medium having the structure shown in FIGS. 41A and 41B. FIG. 41A shows magnetization states of the respective layers before the reproduction. It is assumed that recording magnetic domains 422 are previously written in the magneto-optical recording layer 406 in accordance with the magnetic field modulation system or the optical modulation recording system. When the magneto-optical recording medium is irradiated with the reproducing light beam having an appropriate power so that the maximum arrival temperature of the magnetic layer is a desired temperature which is less than TC0, the recording magnetic domain 422 in the magneto-optical recording layer 406 is transferred as a magnetic domain 421 to an area in the first auxiliary magnetic layer 405 in which the temperature is not less than TCR1 as shown in FIG. 41B. In this process, as described later on, it is preferable that the size of the magnetic domain 421 is smaller than the size of the recording magnetic domain 422 of the magneto-optical recording layer 406, i.e., the recording magnetic domain 422 is reduced and transferred to the first auxiliary magnetic layer 405. Subsequently, the magnetic domain 421, which has been transferred to the first auxiliary magnetic layer 405, is transferred as a magnetic domain 423 to the second auxiliary magnetic layer 404.
FIG. 45 shows, in its upper part, a temperature distribution obtained when the magneto-optical recording medium having the structure shown in FIG. 41B is heated by the reproducing laser spot (LS). FIG. 45 shows, in its middle part, a temperature distribution of the magneto-optical recording medium with respect to the laser spot (LS) as viewed from a position over the second auxiliary magnetic layer. The magneto-optical recording medium is set so that the critical temperatures of the first and second auxiliary magnetic layers satisfy TCR2 less than TCR1. Therefore, the temperature area in which the temperature exceeds TCR2, i.e., the area of the second auxiliary magnetic layer capable of providing the perpendicular magnetization state is larger than the temperature area in which the temperature exceeds TCR1, i.e., the area in the first auxiliary magnetic layer capable of providing the perpendicular magnetization state. Therefore, the magnetic domain 423, which is transferred to the second auxiliary magnetic layer 404, is magnified to be larger than the size of the magnetic domain 421, owing to the perpendicular magnetic anisotropy of the second auxiliary magnetic layer and the exchange coupling force from the transferred magnetic domain of the first auxiliary magnetic layer 405. The magnified magnetic domain 423 is larger than the recording magnetic domain 422 in the magneto-optical recording layer 406. Therefore, the reproduced signal, which is detected in accordance with the magneto-optical effects (Kerr effect and Faraday effect), is amplified as compared with a case of detection from the magnetic domain having the same size as that of the recording magnetic domain 422. Thus, it is possible to perform the reproduction at high C/N. That is, the amplitude of the reproduced signal from the minute magnetic domain is extremely small in the case of production based on the use of the ordinary magnetically induced super resolution. However, when the magneto-optical recording medium referred to herein is used, it is possible to obtain the amplified amplitude of the reproduced signal even if the signal is reproduced from the minute magnetic domain.
In the magneto-optical recording medium according to the present invention, it is preferable that the size of the magnetic domain 421 transferred to the first auxiliary magnetic layer 405 is smaller than that of the recording magnetic domain 422 in the magneto-optical recording layer 406. That is, it is preferable that the magnetic domain is reduced when the recording magnetic domain 422 in the magneto-optical recording layer 406 is transferred as the magnetic domain 421 to the first auxiliary magnetic layer 405. The reason for the above will be explained below.
If the size of the magnetic domain 421 (magnetization in the direction ↑) transferred to the first auxiliary magnetic layer 405 is equivalent to or larger than the size of the recording magnetic domain 422, then the magnetic domain 421 is magnetically affected by the magnetic domain S having the magnetization in the direction ↓ adjacent to the recording magnetic domain 422, and the magnetic domain 421 becomes unstable. It is necessary that the magnetic domain 421, which is transferred to the first auxiliary magnetic layer 405, plays a role to transfer the magnetization information of the recording magnetic domain 422 to the second auxiliary magnetic layer 404 which functions to magnify the magnetic domain. Therefore, it is necessary that the magnetic domain 421 is magnetically stable. Accordingly, when the magnetic domain is reduced and transferred from the recording magnetic domain 422 to the first auxiliary magnetic layer 405, it is possible to reduce the influence from the magnetic domain S adjacent to the recording magnetic domain 422 on the magnetic domain 421 of the first auxiliary magnetic layer 405. Accordingly, the magnetization of the magnetic domain 421 of the first auxiliary magnetic layer 405 can be stabilized. Especially, the magneto-optical recording medium is subjected to the reproduction in a state of being rotated in ordinary cases. Therefore, as shown in FIGS. 41A and 41B, the magnetic domains in the magneto-optical recording layer 406 are successively moved with respect to the reproducing light beam spot in accordance with the rotation of the magneto-optical recording medium. On the other hand, the temperature area of the first auxiliary magnetic layer 405, in which the temperature exceeds TCR1, exists at the constant position with respect to the reproducing light beam spot. If the temperature area of the first auxiliary magnetic layer 405, in which the temperature exceeds TCR1, has the same size as that of the recording magnetic domain 422, only one recording magnetic domain 421 exists in the temperature area merely instantaneously during the movement. During the period of time other then the above, those which exist in the temperature area include a part of one magnetic domain 421 and a part of the recording magnetic domain having the in-plane magnetization adjacent thereto. Therefore, it is extremely difficult to read only the magnetization information of the single recording magnetic domain from the temperature area of the first auxiliary magnetic layer 405 in which the temperature exceeds TCR1. However, when the temperature area of the first auxiliary magnetic layer 405, in which the temperature exceeds TCR1, is smaller than the size of the recording magnetic domain 422, the temperature area exists over only the single recording magnetic domain for a relatively long period of time. The magnetic domain 421, to which the magnetization of the recording magnetic domain 422 is transferred owing to the fact that the temperature exceeds TCR1, is completely included in the upward area of the recording magnetic domain 422 in an instant shown in FIG. 51A and in an instant shown in FIG. 51B as well. Therefore, the magnetization information can be reliably transferred from the recording magnetic domain 422 to the first auxiliary magnetic layer 405. The foregoing reason holds true even when the first auxiliary magnetic layer behaves as a perpendicularly magnetizable film at a temperature of not less than room temperature. That is, it is effective to perform the transfer so that the magnetic domain, which is transferred from the magneto-optical recording layer to the first auxiliary magnetic layer, is reduced, even in the case of the use of a magnetic material as the first auxiliary magnetic layer which exhibits the perpendicular magnetization at a temperature of not less than room temperature.
The decrease in size of the magnetic domain 421 transferred to the first auxiliary magnetic layer 405 as compared with the recording magnetic domain 422 in the magneto-optical recording layer 406 is also effective because of the following reason. The recording magnetic domain S having the magnetization in the direction ↓ exists adjacent to the recording magnetic domain 422 having the magnetization in the direction ↑. However, the first auxiliary magnetic layer 405 has the in-plane magnetization in the ranges indicated by the areas W shown in FIG. 45. Therefore, the exchange coupling force, which is exerted on the second auxiliary magnetic layer 404 from the magnetic domain S of the magneto-optical recording layer 406 in the direction ↓, is intercepted by the in-plane magnetization. Accordingly, the in-plane magnetization of the first auxiliary magnetic layer 405 effectively acts to magnify the magnetic domain 423. When the size of the magnetic domain in the first auxiliary magnetic layer 405 is smaller than the size of the recording magnetic domain 422, it is possible to further increase the effect to intercept the exchange coupling force exerted by the in-plane magnetization of the first auxiliary magnetic layer 405 from the magnetic domain S in the direction ↓ to the second auxiliary magnetic layer 404. Accordingly, it is easier to perform the magnetization of the magnetic domain 422 (magnetization in the direction ↑).
In order to decrease the size of the magnetic domain in the first auxiliary magnetic layer 405 to be smaller than the size of the recording magnetic domain 422, it is preferable that the laser power and TCR1 of the first auxiliary magnetic layer 405 are adjusted so that the temperature area of the first auxiliary magnetic layer 405, in which the temperature exceeds TCR1, is smaller than the size (width) of the recording magnetic domain 422 in the magneto-optical recording layer 406 as shown in FIG. 45. In the example shown in FIG. 45, the laser power and TCR2 of the second auxiliary magnetic layer 404 are further adjusted so that the temperature area of the second auxiliary magnetic layer 404, in which the temperature exceeds TCR2, is larger than the size (width) of the recording magnetic domain 422. Therefore, during the reproduction, the recording magnetic domain 422 in the magneto-optical recording layer 406 is reduced and transferred as the magnetic domain 421 to the first auxiliary magnetic layer 405. The magnetic domain 421 is further magnified and transferred as the magnetic domain 423 to the second auxiliary magnetic layer 404.
The fact that the size of the magnetic domain 421 transferred to the first auxiliary magnetic layer 405 is smaller than the recording magnetic domain 422 in the magneto-optical recording layer 406 can be verified, for example, by means of the following method. The substrate 401 is removed from the magneto-optical recording medium shown in FIG. 40 on which information is recorded. The dielectric film 403 and the second auxiliary magnetic film 404 are removed, for example, by means of the sputtering etching. The surface of the first auxiliary magnetic film may be heated to a reproducing temperature to perform observation with an optical microscope or the like.
The effect of the amplification of the reproduced signal, which is brought about by the magnification of the magnetic domain 423 of the second auxiliary magnetic layer 404, is maximized when the transferred magnetic domain in the second auxiliary magnetic layer 404 is magnified up to the radius of the reproducing light beam spot. In this state, the magnitude of the reproduced signal depends on the reproducing light beam and the performance index such as the Kerr effect of the second auxiliary magnetic layer 404, irrelevant to the size and the shape of the recording magnetic domain 422 of the magneto-optical recording layer 406. The area of the magneto-optical recording medium, from which information is read, has a temperature lowered to be less than TCR2 after the spot of the reproducing light beam passes thereover. The perpendicular magnetization of the first and second auxiliary magnetic layers is returned to the in-plane magnetization, giving the state shown in FIG. 41A again. During the reproduction operation as described above, the power of the reproducing light beam is adjusted so that the maximum arrival temperature of the magneto-optical recording medium is lower than the Curie temperature TC0 of the magneto-optical recording layer 406. Therefore, the magnetization information, which is recorded in the magneto-optical recording layer 406, is not affected by the reproducing light beam.
It is necessary for the magneto-optical recording medium according to the fifth aspect that the thickness of the first auxiliary magnetic layer is not less than the thickness of the magnetic wall of the first auxiliary magnetic layer. As shown in FIGS. 41A, 41B, and 45, when the temperature exceeds the critical temperature TCR1, the magnetization of the first auxiliary magnetic layer 405 undergoes the transition from the in-plane magnetization to the perpendicular magnetization. In order to enable the transition, it is necessary that the magnetic spin is twisted by 90 degrees in the magnetic wall (hereinafter referred to as xe2x80x9cmagnetic wall of the first auxiliary magnetic layerxe2x80x9d) between the magnetic domain 421 in the first auxiliary magnetic layer 405 and the magnetic domain of the in-plane magnetization of the first auxiliary magnetic layer 405 adjacent to the magnetic domain 421. Further, it is necessary that only the first auxiliary magnetic layer behaves as the in-plane magnetizable film in the area W to mitigate the spin of the magneto-optical recording layer 406 and the second auxiliary magnetic layer. Therefore, in order to allow the transition between the in-plane magnetization and the perpendicular magnetization in the first auxiliary magnetic layer 405, it is required that the thickness of the first auxiliary magnetic layer 405 is, at the minimum, not less than the thickness of the magnetic wall of the first auxiliary magnetic layer 405. The thickness of the magnetic wall can be measured by using the Hall effect in the same manner as described above.
As described above, the thickness of the magnetic wall differs depending on the type and the composition of the magnetic material. However, the thickness of the magnetic wall is generally required to be 10 nm at the minimum for the magnetic material to be used for the magnetic layer of the magneto-optical recording medium. Therefore, according to the eleventh aspect of the present invention, it is preferable that the thickness of the first auxiliary magnetic layer is a thickness which exceeds 10 nm. The upper limit of the first auxiliary magnetic layer is preferably not more than 100 nm in view of the restriction of the power of the semiconductor laser as the reproducing light source. Therefore, the thickness t of the first auxiliary magnetic layer preferably satisfies 10 less than t less than 100 nm.
The magneto-optical recording medium according to the seventh aspect is a magneto-optical recording medium comprising a magneto-optical recording film and an auxiliary magnetic film, for reproducing a signal by magnetically transferring a recording magnetic domain in the magneto-optical recording film to the auxiliary magnetic film when the magneto-optical recording medium is irradiated with a reproducing light beam, wherein the auxiliary magnetic film is a magnetic film composed of at least one layer for making transition from an in-plane magnetizable film to a perpendicularly magnetizable film when a temperature of the auxiliary magnetic film exceeds a critical temperature, the magneto-optical recording film is a perpendicularly magnetizable film at a temperature of not less than room temperature, and a magnetic characteristic of the auxiliary magnetic film is utilized to make it possible to transfer a magnetic domain larger than the recording magnetic domain of the magneto-optical recording film to the auxiliary magnetic film during reproduction.
One type of the magneto-optical recording medium according to the seventh aspect has the following magnetic characteristic. That is, as shown in FIG. 41A and FIG. 41B, the magneto-optical recording medium has a structure comprising a first auxiliary magnetic film 405 and a second auxiliary magnetic film 404 stacked successively on a magneto-optical recording film 406. The magneto-optical recording film 406, the first auxiliary magnetic film 405, and the second auxiliary magnetic film 404 satisfies a relationship of room temperature  less than TCR2 less than TCR1 less than TC0, TC1, TC2 provided that the Curie temperatures of the magneto-optical recording film 406, the first auxiliary magnetic film, and the second auxiliary magnetic film are TC0, TC1, and TC2 respectively, and the critical temperatures of the first auxiliary magnetic film and the second auxiliary magnetic film are TCR1 and TCR2 respectively. As shown in FIG. 42, the first auxiliary magnetic film 405 and the second auxiliary magnetic film 404 have the following magnetic characteristic. That is, each of them is an in-plane magnetizable film from room temperature to a certain critical temperature (TCR) which is not less than room temperature, and it behaves as a perpendicularly magnetizable film at a temperature which is not less than TCR. The magneto-optical recording film 406 is a perpendicularly magnetizable film at a temperature which is not less than room temperature.
The principle of the operation (reproduction) on the magneto-optical recording medium used in the seventh aspect will be explained below. FIG. 41A shows magnetization states of the respective layers before the reproduction, after the recording magnetic domains are written in the magneto-optical recording film 406, for example, in accordance with the optical modulation recording system. When the medium is irradiated with the reproducing light beam having an appropriate power so that the maximum arrival temperature of the magnetic film is a desired temperature, the magnetic domain 422 of the perpendicular magnetization in the magneto-optical recording film 406 is firstly transferred to an area in the first auxiliary magnetic film 405 in which the temperature is not less than TCR1. During this process, considering the temperature profile in the medium obtained when the reproducing light beam is radiated as shown in FIG. 54, the reproducing power and TCR1 are set so that the magnetic domain 422, which has the same size as that of the magnetic domain in the magneto-optical recording film 406 or which is smaller than the magnetic domain in the magneto-optical recording film 406, is transferred to the first auxiliary magnetic film 405.
Subsequently, the magnetic domain 422, which is transferred to the first auxiliary magnetic film 405, is transferred to the ,second auxiliary magnetic film 404. In the present invention, the first and second auxiliary magnetic films are set so that their critical temperatures satisfy TCR2 less than TCR1. Therefore, as shown in the temperature profile in the medium in FIG. 54, the area in the second auxiliary magnetic film, which is able to be in the perpendicular magnetization state, has a radius larger than that in the first auxiliary magnetic film. Accordingly, as shown in FIG. 41B, the transferred magnetic domain 423 in the second auxiliary magnetic film 404 is magnified by the perpendicular magnetic anisotropy in the area in the second auxiliary magnetic film which is able to be in the perpendicular magnetization state and the exchange coupling force from the perpendicular magnetization in the first auxiliary magnetic film 405. It is also considered that the magnification of the magnetic domain is facilitated in view of the fact that the in-plane magnetization of the area indicated by W in FIG. 41 in the first auxiliary magnetic film 405 weakens the exchange coupling force from the magnetic domain S of the magneto-optical recording film 406 to the second auxiliary magnetic film 404. The magnification of the magnetic domain described above reduces the decrease in amount of light to contribute to the reproduction output effected by the magnetic mask of the in-plane magnetization. Thus, it is possible to perform the reproduction at a high C/N ratio.
The effect of the magnification of the magnetic domain 423 of the second auxiliary magnetic film 404 is maximized when the transferred magnetic domain in the second auxiliary magnetic film 404 is magnified to be not less than the radius of the reproducing light beam spot. In this state, it is possible to obtain an extremely large reproduction output which is determined by only the light of the reproducing beam and the performance index of the second auxiliary magnetic film 404, irrelevant to the size and the shape of the magnetic domain recorded in the magneto-optical recording film 406. After the reproduction, i.e., after the movement of the radiating section for the reproducing light beam, the reading section is cooled to be not more than TCR2. Each of the first and second auxiliary magnetic films is in the in-plane magnetization state, returning to the state shown in FIG. 41A. The coercive force of the magneto-optical recording film 406 is sufficiently large even at the temperature during the reproducing operation as described above. Therefore, the information recorded as the magnetization is completely held.
As shown in FIG. 53, the magneto-optical recording medium according to the eighth aspect comprises a non-magnetic film 409 disposed between an auxiliary magnetic film 408 and a magneto-optical recording film 406, wherein the magneto-optical recording film 406 and the auxiliary magnetic film 408 have such magnetic characteristics that a relationship of room temperature  less than TCR less than TC0, TC is satisfied provided that Curie temperatures of the magneto-optical recording film 406 and the auxiliary magnetic film are TC0 and TC respectively, and a critical temperature of the auxiliary magnetic film is TCR.
Explanation will be made for the principle of reproduction on the magneto-optical recording medium used in the eighth aspect. FIG. 52A schematically shows the magnetization state of the auxiliary magnetic film 408, the non-magnetic film 409, and the magneto-optical recording film 406 before performing the reproduction after the magnetic domains are written into the magneto-optical recording film 406 of the medium shown in FIG. 53, for example, in accordance with the optical modulation recording system. When the magneto-optical recording medium is irradiated with a reproducing light beam having an appropriate power so that the maximum arrival temperature of the magnetic film is a desired temperature, an area appears in the auxiliary magnetic film 408, in which the temperature is not less than TCR, being capable of causing the perpendicular magnetization state. TCR and the reproducing power are set so that the size of the area is not less than the radius of the magnetic domain M recorded in the magneto-optical recording film 406, preferably not less than the radius of the reproducing light beam spot. The coercive force of the auxiliary magnetic film 408 is distributed as shown in FIG. 55 corresponding to the temperature distribution in the area in which the temperature is not less than TCR, having such a magnetic characteristic that the value is sufficiently small in the area in which the temperature arrives at the maximum arrival temperature and in the vicinity thereof.
The magneto-optical recording film 406 has its distribution of magnetization as shown in FIG. 55 corresponding to the temperature distribution in the area in which the temperature is not less than TCR, having such a magnetic characteristic that the value is sufficiently large in the area in which the temperature arrives at the maximum arrival temperature and in the vicinity thereof. The magnetic characteristics of the respective magnetic films are set as described above. Therefore, only the magnetic domain M in the magneto-optical recording film 406, which is located in the area in which the temperature is high and the magnetization is sufficiently large, is transferred to the area in the auxiliary magnetic film 408 in which the temperature is high and the coercive force is sufficiently small, by the aid of the large magnetostatic coupling force between the magneto-optical recording film 406 and the auxiliary magnetic film 408 acting in the area of the magnetic domain M. Accordingly, it is possible to certainly obtain sufficient reproducing resolution.
Subsequently, the magnetic domain 463, which is transferred to the auxiliary magnetic film 408, is considered to be magnified as shown in FIG. 52B, by the aid of perpendicular magnetic anisotropy in the area in which the temperature is not less than TCR and the exchange coupling force exerted by the transferred magnetic domain. Owing to the magnification of the magnetic domain, the reproduced signal is enhanced in the same manner as in the magneto-optical recording medium of the first type, and C/N is improved. After the reproduction, i.e., after the reproducing laser beam is moved, the reading section is cooled so that the temperature is not more than TCR, and the auxiliary magnetic film 408 behaves as the in-plane magnetizable film, returning to the state shown in FIG. 52A.
The principle of the light power-modulating reproducing method according to the present invention will be explained by using a schematic diagram concerning the reproducing method shown in FIG. 57. In this reproducing method, the magneto-optical recording medium of the second type shown in FIG. 52 is used. At first, a predetermined recording pattern as shown in FIG. 57(a) is recorded on the second type magneto-optical recording medium as the magneto-optical recording medium by using, for example, the optical modulation recording system. In FIG. 57(a), the recording mark is recorded at a shortest mark pitch DP, and the recording mark length DL is set to give DL=DP/2. Upon reproduction, a pulse laser beam, which is modulated to have two kinds of reproducing powers Pr2, Pr1, is used as the reproducing laser beam to be radiated so that the cycle which synchronized with the recording mark position is DP, and the light emission width of the high power Pr2 is DL as shown in FIG. 57(b). The light beam having the low reproducing power Pr1 is always radiated in an erasing state (onto portions at which no recording mark exists), and the light beam having the high reproducing power Pr2 is radiated in a recording state (onto portions at which the recording mark exists) and in the erasing state.
FIG. 57(c) illustrate a reproduced signal waveform obtained by radiating the reproducing pulse laser as shown in FIG. 57(b). On the other hand, FIG. 57(d) illustrates a reproduced signal waveform obtained when the same track is subjected to reproduction by using a continuous light beam having a constant reproducing light power. Pr2 and Pr1 are selected as follows. That is, Pr2 is a recording power to cause the magnification of the magnetic domain in the auxiliary magnetic film 408 as described later on. Pr1 is a power to extinguish the magnified magnetic domain. When the reproducing power is selected as described above, the amplitude Hpl, which is provided between the recording state and the erasing state observed during the reproduction with the pulse light beam, is allowed to satisfy Hpl greater than Hdc with respect to the amplitude Hdc obtained upon the reproduction with the constant laser beam. Further, the magnetization information, which is recorded in each of the magnetic domains of the magneto-optical recording film 406, can be independently magnified and reproduced without being affected by adjacent magnetic domains.
When the magneto-optical recording medium according to the eighth aspect is subjected to the reproduction, it is preferable that the light power Pr1 of the reproducing light beam is such a power that the auxiliary magnetic film is heated to a temperature of Tcr to Tcomp, the recording magnetic domain in the magneto-optical recording film 406 is transferred to the auxiliary magnetic film, and the magnetic domain is magnified, and the light power Pr2 of the reproducing light beam is such a power that the auxiliary magnetic film is heated to a temperature of Tcomp to Tco to reduce or extinguish the magnified magnetic domain.
The magneto-optical recording medium according to the ninth aspect is a magneto-optical recording medium having at least a magneto-optical recording film 406 on a substrate, the magneto-optical recording medium comprising the magneto-optical recording film 406 having perpendicular magnetization and an auxiliary magnetic film to cause transition from an in-plane magnetizable film to a perpendicularly magnetizable film when a temperature exceeds a critical temperature Tcr with a non-magnetic film intervening therebetween, wherein a relationship of room temperature  less than Tcr less than Tcomp less than Tco less than Tc holds concerning a Curie temperature Tco of the magneto-optical recording film 406 and a Curie temperature Tc and a compensation temperature Tcomp of the auxiliary magnetic film, and wherein under a condition in which an external magnetic field Hex is applied to the magneto-optical recording medium, a temperature curve A of a transfer magnetic field which is generated by the external magnetic field Hex and the magneto-optical recording film 406, and a temperature curve B of a coercive force of the auxiliary magnetic film in a perpendicular direction intersect at a point between room temperature and the compensation temperature Tcomp of the auxiliary magnetic film, and the temperature curve A and the temperature curve B intersect at a point between the compensation temperature Tcomp of the auxiliary magnetic film and the Curie temperature Tco of the magneto-optical recording film 406.
Explanation will be made for the principle of the reproducing method on the magneto-optical recording medium according to the ninth aspect. The reproducing method is based on the use of the magneto-optical recording medium comprising the magneto-optical recording film 406 having the perpendicular magnetization, and the auxiliary magnetic film which causes transition from the in-plane magnetizable film to the perpendicularly magnetizable film when the temperature exceeds the critical temperature Tcr, with the non-magnetic film interposed therebetween. FIG. 64 shows an illustrative structure of the magneto-optical recording medium of this type. A magneto-optical disk 490 shown in FIG. 64 comprises, in a stacked form on a substrate 401, a dielectric film 403, an auxiliary magnetic film 408, a non-magnetic film 409, a magneto-optical recording film 406, and a protective film 407. The auxiliary magnetic film 408 has a compensation temperature Tcomp between a critical temperature Tcr and its Curie temperature Tc. The magneto-optical recording medium 490 satisfies the relationship of room temperature  less than Tcr less than Tcomp less than Tco less than Tc concerning the Curie temperature Tco of the magneto-optical recording film 406, the critical temperature Tcr, the Curie temperature Tc, and the compensation temperature Tcomp of the auxiliary magnetic film 408.
Reproduction is performed in accordance with the reproducing method of the present invention by radiating the light power-modulated reproducing light beam while applying the external DC magnetic field to the magneto-optical recording medium 490 having the magnetic characteristic as described above. FIG. 66 shows magnetic characteristics of the magneto-optical recording film 406 and the auxiliary magnetic film 408 of the magneto-optical disk 490 in a state in which the constant DC magnetic field Hex is applied to the magneto-optical recording medium 490 in the recording direction. The magnetic temperature curve A shown in FIG. 66 denotes a temperature-dependent change in transfer magnetic field (static magnetic field) generated by the magnetization of the recording layer from the magneto-optical recording film 406 (hereinafter simply referred to as xe2x80x9crecording layerxe2x80x9d) to the auxiliary magnetic film 408 (hereinafter simply referred to as xe2x80x9creproducing layerxe2x80x9d). The transfer magnetic field of the curve A represents the magnitude of the magnetic field obtained by adding an amount of offset of the external magnetic field Hex. Therefore, the magnetic filed having the magnitude of (Hexxe2x88x92Ht) and the magnetic field having the magnitude of (Hex+Ht) exist as the entire transfer magnetic field depending on the direction of the magnetic domain of the recording layer, with a boundary of the Curie temperature Tco of the recording layer. The two magnetic fields constitute the curve A. In FIG. 66, the downward direction is the recording direction. Hex is also applied in the downward direction. In this case, the external magnetic field Hex is adjusted to be small as compared with the magnitude of the static magnetic field Ht in the initializing direction generated from the magnetization of the recording layer at room temperature. Therefore, the entire transfer magnetic field includes those directed in the upward direction (negative) and in the downward direction (positive) depending on the magnetization direction of the recording magnetic domain in the recording layer as illustrated by the curve A.
The magnetic temperature curve B denotes the temperature-dependent change of the coercive force in the perpendicular direction of the reproducing layer in a state of having the perpendicular magnetization. The coercive force is represented by Hr+Hw as including the pure coercive force Hr of the magnetic domain in the reproducing layer in the perpendicular direction and the magnetic field Hw corresponding to a virtual magnetic field regarded to be applied by generation of the magnetic wall of the reproducing layer (in other words, the exchange coupling magnetic field in the in-plane direction of the reproducing layer). That is, Hr+Hw represents the magnetic field necessary to perform inversion of the magnetization in the direction perpendicular to the film surface of the reproducing layer. As shown in FIG. 66, the magnetization in the direction perpendicular to the film surface of the reproducing layer appears at a temperature which is not less than the critical temperature Tcr at which the reproducing layer behaves as a perpendicularly magnetizable film. The coercive force is maximal at the compensation temperature Tcomp because the magnetization of the reproducing layer is zero.
The temperature curves A and B shown in FIG. 66 are divided into those belonging to three areas (a) to (c) as shown in FIG. 66. The three areas (a) to (c) correspond to the three steps of i) magnetic domain transfer from the recording layer to the reproducing layer, ii) magnification of the transferred magnetic domain in the reproducing layer, and iii) extinguishment of the magnified magnetic domain, in the reproducing method of the present invention as shown in FIG. 67A respectively. Accordingly, explanation will be made with reference to FIG. 67 for the magnetic characteristics required for the recording layer and the reproducing layer in the areas (a) to (c) shown in FIG. 66. Arrows in the recording layer and the reproducing layer shown in FIG. 67A denote the direction of the magnetic moment of the rare earth metal included in each of the magnetic domains.
The area (a) is a temperature area in which the magnetic domain is transferred from the recording layer to the reproducing layer in the reproducing method of the present invention, which belongs to a temperature range of T0 to T1 in FIG. 67A. T0 means the critical temperature Tcr, and T1 is a temperature at which the magnetic temperature curve A on the side of Hexxe2x88x92Ht initially intersects the magnetic temperature curve B. The temperature range T0 to T1 can be achieved by adjusting the light power of the reproducing light beam to be a relatively low power as described later on. In order to actually perform the magnetic transfer as shown in FIG. 67A (1) in this temperature area, it is necessary that the magnitude of the transfer magnetic field in this temperature area exceeds the coercive force of the reproducing layer in the perpendicular direction. That is, when the magnetization recorded on the recording layer is in the direction ↓ (recording direction), it is necessary that the transfer magnetic field represented by Hex+Ht is larger than Hr+Hw or xe2x88x92(Hr+Hw) (requirement for magnetic domain transfer). When the magnetization recorded on the recording layer is in the direction ↑ (erasing direction), it is necessary that the negative transfer magnetic field represented by Hexxe2x88x92Ht is smaller than the coercive force Hr+Hw or xe2x88x92(Hr+Hw) of the reproducing layer in the perpendicular direction (requirement for magnetic domain transfer).
On the other hand, when the magnetic temperature curves A and B are compared with each other in the area (a) shown in FIG. 66, it is appreciated that the relationships of the following expressions (a1) to (a3) hold.
Hr less than Hex+Htxe2x88x92Hwxe2x80x83xe2x80x83(a1)
xe2x88x92Hr greater than Hex+Ht+Hwxe2x80x83xe2x80x83(a2)
Hr greater than Hexxe2x88x92Htxe2x88x92Hwxe2x80x83xe2x80x83(a3)
Therefore, the area (a) satisfies the magnetic domain transfer requirement described above, and the recording magnetic domain in the recording layer can be transferred to the reproducing layer regardless of the direction of magnetization thereof. FIG. 67A (1) shows a case in which the magnetization in the direction ↓ recorded in a magnetic domain 610 in the recording layer is transferred to an area of the reproducing layer at a temperature which exceeds the temperature T0 within the reproducing light spot so that a transferred magnetic domain 601a is formed.
Subsequently, in the area (b) shown in FIG. 66, the magnetic domain magnification is performed for the magnetic domain 601b transferred to the reproducing layer as shown in FIG. 67A (2) and (3). This temperature area resides in a range indicated by T1 to T2 in FIG. 66. The temperature T2 is a temperature at which the magnetic temperature curve A on the side of Hexxe2x88x92Ht intersects the magnetic temperature curve B on the high temperature side. The magneto-optical disk having the magnetic characteristic shown in FIG. 66 is adjusted such that T2 is approximately coincident with the compensation temperature Tcomp of the reproducing layer (the temperature exists between the compensation temperature Tcomp and the Curie temperature Tco of the recording layer, and the temperature is a temperature extremely close to the compensation temperature Tcomp) in relation to the external magnetic field Hex. In this temperature area, as shown in FIG. 67A (2), magnetic domains 603, 603xe2x80x2, which are subjected to magnetic transfer from magnetic domains 612, 612xe2x80x2 in the recording layer in the upward direction, exist on both sides of the magnetic domain 601b transferred to the reproducing layer, as a result of being heated to T0 to T1 within the reproducing light spot. In order to allow the magnetic domain 601b transferred to the reproducing layer to start magnification in the in-plane direction, it is necessary that the directions of the magnetic domains 603, 603xe2x80x2 disposed on the both sides are directed to the recording direction (direction ↓) in the same manner as the magnetic domain 601b. The magnetic domains 603, 603xe2x80x2 receive the transfer magnetic field (Hexxe2x88x92Ht) (totally in the direction ↑) obtained by adding, to the external magnetic field Hex, the static magnetic field Ht in the upward direction from magnetic domains 622 in the recording layer existing just thereover. On the other hand, the magnetic domains 603, 603xe2x80x2 have the coercive force in the perpendicular direction including the exchange coupling magnetic field Hw (in the downward direction) exerted by the magnetic domain 601b and the coercive force Hr to invert the magnetization of the magnetic domains 603, 603xe2x80x2 themselves. Therefore, when the coercive force in the perpendicular direction (Hr+Hw) is made larger than the transfer magnetic field (Hexxe2x88x92Ht) of the magnetic domains 603, 603xe2x80x2, the magnetic domains 603, 603xe2x80x2 are inverted (requirement for magnetic domain inversion).
It is appreciated that the following relational expressions hold in the area (b) according to the relative magnitude between the magnetic temperature curves A and B.
Hr less than Hex+Htxe2x88x92Hwxe2x80x83xe2x80x83(b1)
xe2x88x92Hr less than Hexxe2x88x92Ht+Hwxe2x80x83xe2x80x83(b2)
Hr greater than Hexxe2x88x92Htxe2x88x92Hwxe2x80x83xe2x80x83(b3)
The foregoing expression (b2) is the condition of magnetic domain inversion itself under which the coercive force (Hr+Hw) in the perpendicular direction is larger than the transfer magnetic field Hexxe2x88x92Ht (in the upward direction) of the magnetic domains 603, 603xe2x80x2. Therefore, the magnetic domain magnification occurs in the area (b) for the magnetic domain 601bxe2x80x2 in the reproducing layer as shown in FIG. 66A (3). According to the relationship of (b2), it is demonstrated that no magnetic domain in the downward direction appears in the reproducing layer when there is no magnetic domain in the recording direction in the reproducing layer, in the temperature area (b). In FIG. 66A (3), the both sides of the magnified magnetic domain 601bxe2x80x2 are the temperature area of T0 to T1. Therefore, the magnetic domains 603, 603xe2x80x2 in the direction ↑, which are subjected to the magnetic domain transfer from the magnetic domains 612, 612xe2x80x2 in the recording layer, exist therein.
Subsequently, in the area (c), the transferred and magnified magnetic domain is inverted (extinguished), and a magnetic domain 601c in the erasing direction is formed as shown in FIG. 67A (4). This temperature area exists in a range from T2 which slightly exceeds the compensation temperature of the reproducing layer, to the Curie temperature Tco of the recording layer. The magnified and reproduced magnetic domain can be extinguished or reduced by applying the reproducing magnetic field in the erasing direction, i.e., by using the alternating magnetic field as the reproducing magnetic field. However, in the reproducing method of the present invention, the DC magnetic field is used to extinguish the magnified magnetic domain by power-modulating the reproducing light beam to have the power higher than the reproducing light power used to perform the magnetic transfer and the magnification. The reproducing light power may be modulated to be further small in order to extinguish the magnified magnetic domain, as described in the seventeenth embodiment of the reproducing method on the magneto-optical recording medium according to the present invention as described later on.
Explanation will be made with reference to FIG. 68 for the principle to invert (extinguish) the magnified magnetic domain in the area (c). FIG. 68 illustrates the temperature-dependent change of the direction and the magnitude of sub-lattice magnetization of the rare earth metal and the transition metal of the magnetic domain 620 in the recording layer composed of the rare earth-transition metal (TbFeCo alloy) and the magnetic domain 601b in the reproducing layer composed of the rare earth-transition metal (GdFeCo alloy) subjected to the magnetic domain transfer therefrom shown in FIG. 67 (2). As shown in FIG. 68A, when the temperature of the reproducing layer is less than the compensation temperature Tcomp, then the magnetization of the rare earth metal in the reproducing layer is dominant, and it is parallel to the magnetization direction of the recording layer of the transfer source (the magnetization of the transition metal is dominant). Subsequently, when the temperature of the reproducing layer exceeds the compensation temperature Tcomp by radiating the high power laser in accordance with the reproducing method of the present invention, the magnetic moment of the transition metal in the reproducing layer is dominant. It is appreciated that the following expressions (c1) and (c2) hold according to the relative magnitude of the magnetic temperature curves A and B of the reproducing layer and the recording layer in the area (c) shown in FIG. 66.
xe2x80x83Hr less than Hex+Htxe2x88x92Hwxe2x80x83xe2x80x83(c1)
Hr less than Hexxe2x88x92Htxe2x88x92Hwxe2x80x83xe2x80x83(c2)
That is, the coercive force Hr of the magnetic domain 601b is smaller than the entire magnetic field (Hex+Htxe2x88x92Hw or Hexxe2x88x92Htxe2x88x92Hw) in the recording direction acting on the magnetic domain 601b. As a result, when the temperature of the reproducing layer is not less than the compensation temperature Tcomp (exactly, when it is not less than T2), the dominant magnetic moment of the transition metal is inverted to be directed in the recording direction as shown in FIG. 68B. Therefore, the magnetic moment of the rare earth metal in the downward direction of the magnified magnetic domain 601b shown in FIG. 68A (3) is inverted in the area which is heated to the temperature not less than the temperature of the area (c), i.e., not less than the compensation temperature Tcomp. Thus, the inverted magnetic domain 601c is generated (FIG. 68A (4)). The magnetic domains 601, 601xe2x80x2, which are disposed on the both sides of the inverted magnetic domain 601c, have their temperatures ranging from T1 to T2. Therefore, the magnetic domains 601, 601xe2x80x2 have the same magnetization direction as that of the magnified magnetic domain 601b. 
In the reproducing method described above, the three temperature areas (a) to (c) can be achieved by modulating the reproducing light power to have at least the two power levels Pr1 and Pr2 as shown in FIG. 67B. That is, the light power Pr1 of the reproducing light beam may be the power for heating the auxiliary magnetic layer to the temperature of Tcr to Tcomp and making it possible to transfer the recording magnetic domain in the magneto-optical recording film 406 to the reproducing layer and magnify the magnetic domain. The light power Pr2 of the reproducing light beam may be the power for heating the auxiliary magnetic layer to the temperature of Tcomp to Tco and reducing or extinguishing the magnified magnetic domain as described above. The Pr1/Pr2 power-modulated reproducing light beam is used as the reproducing light beam in synchronization with the reproducing clock. Thus, the recording magnetic domain in the recording layer can be subjected to reproduction through the steps of i) transfer to the reproducing layer, ii) magnification of the transferred magnetic domain, and iii) extinguishment of the magnified magnetic domain.
As shown in FIG. 69, the magneto-optical recording medium according to the tenth aspect has a structure comprising a first auxiliary magnetic film 408, a non-magnetic film 409, and a second auxiliary magnetic film 404 which are successively stacked on a magneto-optical recording film 406, wherein the magneto-optical recording film 406, the first auxiliary magnetic film 408, and the second auxiliary magnetic film 404 have such magnetic characteristics that a relationship of room temperature  less than TCR12 less than TCR11 less than TC0, TC1, TC2 is satisfied provided that Curie temperatures of the magneto-optical recording film 406, the first auxiliary magnetic film, and the second auxiliary magnetic film are TC0, TC11, and TC12 respectively, and critical temperatures of the first auxiliary magnetic film and the second auxiliary magnetic film are TCR11 and RCR12 respectively. The critical temperature represents the temperature represented by TCR at which the state of magnetization of the magnetic film is subjected to the state change from the in-plane magnetization to the perpendicular magnetization or from the perpendicular magnetization to the in-plane magnetization. As shown in FIG. 70, the second auxiliary magnetic film 404 behaves as an in-plane magnetizable film from room temperature to the certain critical temperature (TCR12) of not less than room temperature, and it behaves as a perpendicularly magnetizable film at a temperature of not less than TCR12. As shown in FIG. 70, the first auxiliary magnetic film 408 has such a magnetic characteristic that it behaves as a perpendicularly magnetizable film from room temperature to the certain critical temperature (TCR11) of not less than room temperature, and it behaves as an in-plane magnetizable film at a temperature of not less than TCR11. The magneto-optical recording film 406 is a perpendicularly magnetizable film at a temperature of not less than room temperature.
The principle of the operation (reproduction) on the magneto-optical recording medium according to the tenth aspect will be explained below. FIG. 71A shows magnetization states of the respective layers before the reproduction, after the recording magnetic domains are written in the magneto-optical recording film 406, for example, in accordance with the optical magnetic field modulation recording system. When the medium is irradiated with the reproducing light beam having an appropriate power so that the maximum arrival temperature of the magnetic film is a desired temperature, the magnetic domain 422 of the perpendicular magnetization in the magneto-optical recording film 406 is firstly transferred to an area in the second auxiliary magnetic film 404 in which the temperature is not less than TC12. During this process, considering the temperature profile in the medium obtained when the reproducing light beam is radiated as shown in FIG. 54, the reproducing power and TCR1 are set so that the magnetic domain 621, which has the same size as that of the magnetic domain in the magneto-optical recording film 406 or which is smaller than the magnetic domain in the magneto-optical recording film 406, is transferred to the second auxiliary magnetic film 404.
Subsequently, when the first auxiliary magnetic film 408 arrives at a temperature of not less than TCR1, the first auxiliary magnetic film 408 is changed to have the in-plane magnetization to intercept the leak magnetic field and the magnetic field of the magnetic domain signal of the magneto-optical recording film 406. Accordingly, the influence of the leak magnetic field is avoided for the signal of the magnetic domain 422 transferred to the second auxiliary magnetic film 404. Therefore, it is possible to obtain a reproduced signal having high C/N. In the present invention, the first and second auxiliary magnetic films are designed so that their critical temperatures satisfy TCR12 less than TCR11. Therefore, as shown by the temperature profile in the medium in FIG. 54, the radius is increased in the area in the second auxiliary magnetic film in which the perpendicular magnetization state can be provided. When the magneto-optical recording medium is irradiated with the reproducing light beam having an appropriate power so that the maximum arrival temperature of the magnetic film is a desired temperature, an area arises in the second auxiliary magnetic film 404 (reproducing layer) in which the temperature is not less than TCR12 and the perpendicular magnetization state can be provided. TCR12 and the reproducing power are set and used so that the size of the concerning area is not less than the radius of the magnetic domain M recorded in the magneto-optical recording film 406, preferably not less than the radius of the reproducing light beam spot. The second auxiliary magnetic film 404 (reproducing layer) has such a magnetic characteristic that the coercive force has a distribution as shown in FIG. 55 corresponding to the temperature distribution in the area in which the temperature is not less than TCR12, and the value is sufficiently small in the area in which the temperature arrives at the maximum arrival temperature and in the vicinity thereof. At the point of time at which the perpendicular magnetization state occurs while the temperature is not less than TCR12 in the second auxiliary magnetic film 404 (reproducing layer) by irradiating the magneto-optical recording medium with the reproducing light beam, the magnetization state of the first auxiliary magnetic film 408 is changed from the perpendicular magnetization to the in-plane magnetization at the portion in the first auxiliary magnetic film 408 in which the temperature arrives at a temperature of not less than TCR11. During this process, the transferred magnetic domain (domain) in the second auxiliary magnetic film 404 (reproducing layer) is magnified as shown in FIG. 69C. However, the following condition is required. That is, the magnification is effected to give a size in which the reading can be performed with the reproducing light beam, for example, to be larger than the radius of the reproducing light beam spot. Simultaneously, the state of the magnetization of the first auxiliary magnetic film 408 maintains the state of in-plane magnetization to obtain a necessary temperature difference xcex94T between the critical temperatures TCR12 and TCR11 so that the reproduced signal from the second auxiliary magnetic film 404 is not contaminated with any noise signal such as the leak magnetic field, and the leak magnetic field or the like may be intercepted. It is necessary to select and use a combination of materials for the first auxiliary magnetic film 408 and the second auxiliary magnetic film 404 so that the temperature difference xcex94T as described above may be obtained.
The magneto-optical recording film 406 has its distribution of magnetization as shown in FIGS. 71B and 71C corresponding to the temperature distribution in the area in which the temperature is not less than TCR12, having such a magnetic characteristic that the value is sufficiently large in the area in which the temperature arrives at the maximum arrival temperature and in the vicinity thereof. The magnetic characteristics of the respective magnetic films are set as described above. Therefore, only the magnetic domain M in the magneto-optical recording film 406, which is located in the area in which the temperature is sufficiently high and the magnetization is sufficiently large, is transferred to the area in the auxiliary magnetic film 406 in which the temperature is high and the coercive force is sufficiently small, by the aid of the large magnetostatic coupling force between the magneto-optical recording film 406 and the auxiliary magnetic film 408 acting in the area of the magnetic domain M. Accordingly, it is possible to certainly obtain sufficient reproducing resolution.
Subsequently, the magnetic domain, which is transferred to the second auxiliary magnetic film 404, is considered to be magnified as shown in FIG. 71C, by the aid of the perpendicular magnetic anisotropy in the area in which the temperature is not less than TCR12 and the exchange coupling force exerted by the transferred magnetic domain. Owing to the magnification of the magnetic domain, the reproduced signal is enhanced in the same manner as in the magneto-optical recording medium of the first type, and C/N is improved. After the reproduction, i.e., after the reproducing laser beam is moved, the reading section is cooled to be not more than TCR12, and the second auxiliary magnetic film 404 behaves as the in-plane magnetizable film, returning to the state shown in FIG. 71A.
The effect of magnification of the magnetic domain of the second auxiliary magnetic film 404 is maximized when the transferred magnetic domain in the second auxiliary magnetic film 404 is magnified to be not less than the spot radius of the reproducing light beam. In this state, it is possible to obtain an extremely large reproduction output which is determined by only the reproducing light beam and the performance index of the second auxiliary magnetic film 404, irrelevant to the size and the shape of the magnetic domain recorded in the magneto-optical recording film 406. After the reproduction, i.e., after the section for radiating the reproducing light beam is moved, the reading section is cooled to be not more than TCR12, and the second auxiliary magnetic film is in the in-plane magnetization state, returning to the state shown in FIG. 71A. The coercive force of the magneto-optical recording film 406 is sufficiently large even at the temperature during the reproducing operation as described above. Therefore, the information, which is recorded as magnetization, is completely retained.
An optical element composed of a solid immersion lens can be used as an objective lens for the optical head of the reproducing apparatus of the present invention. Such an optical element is made of a material having a refractive index larger than 1. FIG. 83 shows an example of such an optical element 801. FIG. 83 conceptually illustrates the principle of image formation for the optical element 801. Explanation will be made for the condition to improve the recording density by decreasing the spot radius of the laser beam radiated onto the recording medium 803 to be a smaller spot radius. In general, the spot radius S is defined by the following expression (1).
S=xcex/(2NA)=xcex/(2nxc2x7sinxcex8max)xe2x80x83xe2x80x83(1)
It is assumed that xcex represents the wavelength of the laser beam coming into the optical element 801, NA represents the numerical aperture of the optical element 801, n represents the refractive index of the optical element 801, and xcex8max represents the angle (angle of incidence) formed by the optical axis and the light beam (solid lines in FIG. 83) disposed at the outermost side of the incoming light flux. When the wavelength  greater than  of the laser beam is constant, it is understood that NA may be increased in order to decrease the spot radius S according to the foregoing expression (1). NA is defined by NA=nsinxcex8max. Therefore, in order to obtain large NA, it is necessary to increase the refractive index n and the angle xcex8max. Accordingly, when a material having a high refractive index is used for the optical element 801, the wavelength of the incoming light beam is shortened at the inside of the optical element 801. When the incoming light beam is refracted at the surface of the optical element 801, and it is collected at the inside of the optical element 801, then the angle xcex8max, which is formed by the optical axis and the incoming light beam, can be increased in the optical element 801 as compared with one which is obtained before the light beam comes into the optical element 801.
The optical element 801 is a hemispherical type lens formed by cutting a part of a sphere having a radius r. The cut plane of the optical element 801, i.e., the outgoing plane 801a of the optical element 801 is obtained by the cutting perpendicular to the optical axis of the incoming light beam. The cut position of the optical element 801 is located at r/n from the center of the sphere. The outgoing plane 801a of the optical element 101 is made parallel to the surface 803a of the recording medium 803 when the magneto-optical head, which carries the optical element 801, is allowed to float. When the incoming light beam indicated by the solid lines in FIG. 83 is reflected by the cut plane of the spherical lens of the optical element 801 to converge the incoming light beam toward the point on the outgoing plane 801a, then the optical element 801 functions such that the spot is radiated onto the recording medium 703 arranged on the side of the outgoing plane 801a of the optical element 801 via the evanescent field (air gap). Therefore, it is necessary that the distance between the optical element 801 and the recording medium 803 is within the attenuation distance of the evanescent light. The optical element 801 effects the image formation at the position (on the surface 803a of the recording medium 803) of intersection of broken lines obtained by extending the incoming light beam in the optical element 801 indicated by the solid lines. As described above, as for the optical element 801, NA can be increased to a multiple of square of n by shortening the wavelength xcex of the incoming light beam in the optical element 801 and increasing the angle xcex8max by the refraction at the spherical surface of the optical element 801. In other words, the spot radius of the laser beam can be theoretically decreased up to 1/n2. Accordingly, the optical element 801 functions such that the spot formed on the recording medium 803 is decreased to be smaller than the minimum spot obtained in vacuum.
In the magneto-optical head of the present invention, when the magnetic coil is contained in the slider, the apparatus can be allowed to have a more compact size as compared with the conventional one. When the magnetic coil is arranged at the outer circumference of the optical element 801, then the spacing distance between the recording medium and the magnetic coil is narrowed, and it is enough to use a small current flowing through the magnetic coil when the magnetic field is applied. The optical path of the radiated laser beam is not intercepted. Accordingly, the laser beam can be efficiently radiated onto the recording medium. When the magnetic coil is provided at the position closely to the recording medium as compared with the light-outgoing plane of the optical element 801, the spacing distance between the magnetic coil and the recording medium is decreased. It is possible to suppress the electric power consumption of the recording and reproducing apparatus based on the use of the magneto-optical head constructed as described above. It is desirable to use a film-shaped coil for the magnetic coil. When the magnetic coil is composed of a film-shaped coil, the spacing distance between the recording medium and the magnetic coil can be narrowed. As for the magnetic coil, when the inner diameter of the magnetic coil is decreased to be smaller than the outer diameter of the optical element 801, the external magnetic field can be applied to the recording medium more stably.
It is preferable for the magnetic core to use a magnetic material which transmits the light. Accordingly, the optical path of the laser beam radiated toward the recording medium is not intercepted. Therefore, it is possible to efficiently radiate the laser beam onto the recording medium. The magnetic material includes, for example, transparent ferrite. In the magneto-optical head of the present invention, it is preferable that at least a part of the optical element is made of a magnetic material which transmits the laser beam. When such an arrangement is adopted, it is possible to decrease the number of parts used for the magneto-optical head, and it is possible to realize a compact size of the magneto-optical head. Further, the magnetic material, which transmits the laser beam, may be arranged only at a portion in the vicinity of the center perpendicular to the laser beam-outgoing plane of the optical element. Accordingly, it is possible to improve the positioning accuracy for the external magnetic field.